Fix stream iterator (#7384)

Co-authored-by: Rohit Malhotra <rohitvinodmalhotra@gmail.com>

openhands/controller/agent_controller.py

@@ -93,6 +93,7 @@ class AgentController:
         ChangeAgentStateAction,
         AgentStateChangedObservation,
     )
+    _cached_first_user_message: MessageAction | None = None
 
     def __init__(
         self,
@@ -1206,15 +1207,19 @@ class AgentController:
         Returns:
             MessageAction | None: The first user message, or None if no user message found
         """
-        # Find the first user message from the appropriate starting point
-        user_messages = list(self.event_stream.get_events(start_id=self.state.start_id))
+        # Return cached message if any
+        if self._cached_first_user_message is not None:
+            return self._cached_first_user_message
 
-        # Get and return the first user message
-        return next(
+        # Find the first user message
+        self._cached_first_user_message = next(
             (
                 e
-                for e in user_messages
+                for e in self.event_stream.get_events(
+                    start_id=self.state.start_id,
+                )
                 if isinstance(e, MessageAction) and e.source == EventSource.USER
             ),
             None,
         )
+        return self._cached_first_user_message

tests/unit/test_agent_controller.py

@@ -993,6 +993,7 @@ async def test_first_user_message_with_identical_content():
     """
     Test that _first_user_message correctly identifies the first user message
     even when multiple messages have identical content but different IDs.
+    Also verifies that the result is properly cached.
 
     The issue we're checking is that the comparison (action == self._first_user_message())
     should correctly differentiate between messages with the same content but different IDs.
@@ -1038,6 +1039,20 @@ async def test_first_user_message_with_identical_content():
         second_message.id != first_user_message.id
     )  # This should be False, but may be True if there's a bug
 
+    # Verify caching behavior
+    assert (
+        controller._cached_first_user_message is not None
+    )  # Cache should be populated
+    assert (
+        controller._cached_first_user_message is first_user_message
+    )  # Cache should store the same object
+
+    # Mock get_events to verify it's not called again
+    with patch.object(event_stream, 'get_events') as mock_get_events:
+        cached_message = controller._first_user_message()
+        assert cached_message is first_user_message  # Should return cached object
+        mock_get_events.assert_not_called()  # Should not call get_events again
+
     await controller.close()